1. Field of Invention
The invention relates to the field of rubber-modified cementitious substances. Additionally, some embodiments of the invention relate to the field of modifying cementitious substances using rubber from discarded tires.
2. Description of the Related Art
In the United States, more than 200 million used tires are discarded per year. Currently, approximately 11% of these discarded tires are recycled into civil engineering applications, including rubber-modified concrete (“RMC”). However, RMC is not suitable for many applications because it typically is significantly weaker than a comparable conventional concrete (i.e., concrete that is not rubber-modified). Accordingly, rubber-modified concrete generally is used only in secondary or non-critical structures, such as residential driveways, garages floors, trench bedding, and the like. Researchers have hypothesized that RMC is weaker because rubber particles (e.g., ground tire rubber) bond poorly to cement hydration products. Along this vein, several solutions have been proposed. By way of examples, in one study, researchers treated the rubber particles with sodium hydroxide before incorporating them into Portland cement concrete (PCC). In another study, researchers treated the rubber particles with nitric acid and cellulose ether before incorporating them into PCC. In still another study, the surfaces of the rubber particles were etched (to increase surface area) and then incorporated into concrete. While some success has been reported in increasing the strength of RMC, it has not been enough to significantly expand the range of applications for which RMC is suitable.